Polymer particles

ABSTRACT

Polymer particles made from copolymers of multifunctional (meth)acrylate monomer and multifunctional aromatic monomers are disclosed. Also disclosed are methods of improving the compression characteristics of (meth)acrylate polymer particles by copolymerizing with a multifunctional (meth)acrylate monomer a multifunctional aromatic monomer. The particles are of a size, uniformity, and contain physical characteristics that make them ideally suitable for use as spacers in liquid crystal display devices.

This application is a divisional of copending application Ser. No.09/349,890, filed on Jul. 8, 1999, U.S. Pat. No. 6,187,440, which claimsbenefit of U.S. Provisional application No. 60/100,273, filed Sep. 14,1998.

This invention relates generally to polymeric compositions made frommultifunctional monomers. More particularly, this invention relates topolymeric compositions made from multifunctional (meth)acrylate monomersand multifunctional aromatic monomers.

It is very important to have precise control of the thickness of theliquid-crystal layer in liquid-crystal-based displays. Theliquid-crystal layer acts as an electro-optic light valve that works inconjunction with polarizers to modulate the transmission of lightthrough a display between two states one of off, where the liquidcrystals block substantially all light, and one of on, where the liquidcrystals allow transmission of light. Irregularities in the thickness ofthe liquid-crystal layer, also known as the cell gap, result in unevendisplay performance affecting such properties as contrast,transmittance, and the response time of the liquid-crystal layer to anelectric signal.

Liquid crystal displays have a structure such that two substrates,generally glass or plastic sheets, are disposed opposite to each otherthrough optionally a color filter on the inside surface of the topsubstrate (top is the side toward the viewer), an alignment layer, anelectrode layer, a spacer particle, and a liquid crystal layer. Spacersare used to control the thickness of the liquid crystal layer and aswell as to provide a uniform thickness of the liquid crystal layer overthe entire active area of the display. Other means for controlling thecell gap include the flatness of the substrate material, the flatness ofthe layers between the substrates, the number of spacer particles in anygiven area, and the spatial distribution of spacer particles withrespect to one another.

Particles generally suitable for use as spacers in liquid crystaldisplays are chosen from among glass; oxides of silica, alumina or otherceramics; and plastics. The shape of particles generally suitable foruse as spacers in liquid crystal displays are chosen from amongcylindrical rods having aspect ratios from about 1:2 to greater than1:10, and spherical balls. The choice of spacer particles is largelydictated by the characteristics of the spacer particles that include butare not limited to: uniformity of the particle diameter, amount ofimpurities that may leach into the liquid crystal layer, compatibilitywith the liquid crystal layer, hardness, compressibility, coefficient ofthermal expansion, elastic modulus, refractive index, thermal stability,and dielectric constant.

In addition to maintaining the cell gap, spacer particles are veryimportant in establishing the correct cell gap during the assembly ofliquid crystal displays. The liquid-crystal display assembly processgenerally requires the following steps: a) spacer particles aredeposited in a pre-determined concentration onto one sheet of glass orplastic substrate, b) a sealant is applied along the edge of the samesubstrate in a fashion similar to a picture frame leaving a small gapthat will later be used to fill the liquid crystal material, c) a secondsheet of glass or plastic substrate is placed over the first substratecontaining the spacer particles and the adhesive, d) the two substratesare pressed together at an elevated temperature to cure the adhesive andtherefore sealing the substrates together. The properties of the spacerparticles must be such that the particles do not degrade during theapplication of heat and pressure in the sealing process; the spacerparticles must have sufficient thermal stability to withstand heatingand also good compression strength so as to not break or fracture underload.

Plastic spacers will deform in the edge-sealing process described above.The extent of deformation can vary significantly, and is a function ofthe composition of the spacer, the amount of pressure applied during thesealing process, and the heat applied during the sealing process. It ispreferred that a plastic spacer deform slightly when exposed to heat andpressure and then recover some or all of its original shape when theheat and pressure are removed. The extent of recovery, or alternatively,the extent to which the spacer particle is deformed and then resumessome or all or its original diameter, is known as the recovery factor.The recovery factor is described in detail in W.O. Pat. Appl. No.9206402, see in particular FIG. 4 of the cited patent application. Inthe measurement of recovery factor a given load is applied to a spacerparticle and the displacement of the spacer caused by the load ismeasured (L₁). The load is then removed and the extent to which theoriginal particle diameter recovers is given as (L₂). The recoveryfactor is calculated by (L₂/L₁). In view of the variations in displayquality, there is a continuing need for spacer particles that have abalance of properties affecting control of the cell gap during, andafter, the cell sealing process and impacting both the thermal stabilityand the recovery factor of the spacer.

W.O. Pat. Appl. No. 9206402 discloses spheres with certain elasticmodulus and recovery factor properties. The spheres may be applied asspacers for liquid-crystal display elements. The spheres are made ofpolydivinylbenzene, divinylbenzene-styrene copolymer,divinylbenzene-acrylate copolymers, or polydiallylphthalate.

U.S. Pat. No. 5,231,527 discloses a liquid crystal display with twosheets of substrates disposed opposite to each other, transparentelectrodes, orientation films, a spacer particle with a certain range ofelastic modulus, and a liquid crystal layer. The spacer particle may bemade of a crosslinked vinyl copolymer.

U.S. Pat. No. 5,846,657 (Wu) discloses spacer particles with certaincompression values and recovery factors. The particles are polymers of a1,4-butanediol diacrylate or 1,6-hexanediol diacrylate. These particleshave a high compression strength such that they withstand high loadsbefore breaking. However, these particles have a low initial compressionstrength, such that the load these particles can withstand beforedeforming 10% of their original size is limited. A high initial loadcompression strength is important because it allows for the use of fewerparticles to achieve the same result.

Despite the teachings of the disclosures, there is a continuing need toprovide improved spacer particles of uniform size which, and whichpossess, desirable physical characteristics.

The present invention is directed to a plurality of polymer particlescomprising a copolymer of 1 to 30% wt, based on the total weight of themonomers in the copolymer, of a multifunctional (meth)acrylate monomerand 70 to 99% wt, based on the total weight of the monomers in thecopolymer, of a multifunctional aromatic monomer, said particle having aparticle size of 1 to 15 microns with a standard deviation of less than4% of the mean diameter; and a recovery factor greater than 35%.

The present invention is also directed to a method of improving thecompression characteristics of a (meth)acrylate polymer particle bycopolymerizing with a multifunctional (meth)acrylate monomer from 1 to99%, based on the total weight of the monomers in the copolymer, of amultifunctional aromatic monomer.

The present invention is further directed to a liquid crystal displaycontaining a spacer particle formed from a copolymer of 1 to 30% wt,based on the total weight of the monomers in the copolymer, of amultifunctional (meth)acrylate monomer and 70 to 99% wt, based on thetotal weight of the monomers in the copolymer, of a multifunctionalaromatic monomer.

As used throughout the specification, multifunctional monomers areunderstood to contain two or more polymerizable groups. Suitablemultifunctional monomers may contain two, three, four or morepolymerizable groups. As used herein, the term “(meth)acrylate” refersto methacrylate and acrylate.

Suitable multifunctional (meth)acrylate monomers include, but are notlimited to, (C₂-C₁₈)alkanediol di(meth)acrylates. It is preferred thatthe multifunctional (meth)acrylate monomers are (C₂-C₁₀)alkanedioldi(methacrylates, and more preferably (C₄-C8)alkanediol (meth)acrylates.Suitable (C₂-C₁₈)alkanediol (di(meth)acrylates include, but are notlimited to: 1,2-ethanediol di(meth)acrylate; 1,3-propanedioldi(meth)acrylate; 1,4-butanediol di(meth)acrylate; 1,5-pentanedioldi(meth)acrylate; 1,6-hexanediol di(meth)acrylate; 1,8-octanedioldi(meth)acrylate; and 1,10-decanediol di(meth)acrylate. Especiallypreferred are the di-functional acrylate monomers 1,6-hexanedioldiacrylate (“HDDA”); 1,4-butanediol diacrylate (“BDDA”); and mixturesthereof. As used throughout this specification, it is understood thatmixtures of the various (meth)acrylate monomers are within the scope ofthe invention. The following abbreviations are used throughout thespecification: C=centigrade; ml=milliliter; μm=micron; wt %=weightpercent; and ASTM=American Society of Testing Materials.

Suitable multifunctional aromatic monomers are any aromatic monomersthat have two or more polymerizable groups and can be copolymerized withthe multifunctional (meth)acrylate monomers. Suitable multifunctionalaromatic monomers include, but are not limited to: divinylbenzene;divinylnaphthalene; diallyl phthalate and N,N-divinyl aniline.Divinylbenzene is the preferred multifunctional aromatic monomer. Asused throughout this specification, it is understood that mixtures ofthe various aromatic monomers are within the scope of the invention.

Other multifunctional monomers may optionally be copolymerized with the(meth)acrylate monomers and aromatic monomers of the present invention.Suitable optional multifunctional monomers include, but are not limitedto: divinyl sulfide; divinyl solfone; diallyl acrylamide; triallyl(iso)cyanurate; divinyloxybutane; divinyl ether; diallyl maleate; allylacryloxypropionate; 2,2′-bis(4-(meth)acryloxypropyloxyphenyl)propane;2,2′-bis(4-(meth)acryloxydiethoxyphenyl)propane; and triallyltrimellitate.

The polymer particles of the present invention are prepared in amulti-step process which includes: 1) the emulsion polymerization of apre-seed particle, which is preferably mildly crosslinked; 2) emulsionpolymerization of pre-seed particles to form seed particles; 3) swellingof the seed particles with monomers and polymerizing said monomers toform highly-crosslinked polymer particles; and 4) the optionalincorporation of adhesive properties, conductive coatings or colorantsto the particles. A description of such emulsion polymerizationtechniques is disclosed in U.S. Pat. No. 5,846,657 (Wu), hereinincorporated by reference to the extent it teaches emulsionpolymerization of such particles.

It is preferred that the particles of the present invention be curedafter polymerization. Such curing improves the compression resistance ofthe particles. Curing may be by any suitable means, such as chemical orheat curing. Heat curing is preferred. When the particles are heatcured, they may be cured in the reactor after polymerization, or may becured in an oven.

The particles may be heat cured at any temperature from 100° C. up to10° C. below the decomposition temperature of the copolymer. Forexample, if a copolymer decomposes at 200° C., the maximum temperaturefor heat curing would be 190° C. It is preferred that the particles becured at a temperature no higher than 20° C. below their decompositiontemperature. Suitable temperatures for heat curing the particles of thepresent invention are from 100° C. to 320° C., preferably from 100° to250° C., and more preferably from 120° to 200° C. Typically, the polymerparticle is held at the curing temperature for 0.5 to 6 hours, andpreferably from 1 to 4 hours.

The final diameter of the polymer particles of the present invention istypically from about 1.0 to 15.0 microns, more preferably from 3.0 to10.0 microns, and most preferably from about 4.0 to 7.0 microns. One ofthe advantages of the particles of the present invention is that theyhave a very narrow particle-size distribution.

The particle size distribution is such that the standard deviation ofthe particle size is typically 4% or less of the mean diameter,preferably the standard deviation of the particle size is 3% or less ofthe mean diameter and most preferably the standard deviation of theparticle size is 2% or less of the mean diameter. Surprisingly thepresent invention provides for a standard deviation that is invariantwith particle size diameter, such that a particle with a diameter of onemicron has substantially the same standard deviation based on diameteras a particle with a diameter of five microns and additionally aparticle with a diameter of ten microns. Previous disclosures havestandard deviations of particle size that vary with varying particlediameter. Previous disclosures have standard deviations ranging from4.5% to 7.0% based upon particle diameter for diameters ranging from 3.0microns to 11 microns, respectively.

A further advantage of the present invention is the substantialelimination of classification processes to produce the narrow particlesize distributions described hereinabove. The narrow particle sizedistribution is surprisingly inherent to the process of making thespacer particles. The removal of aggregates and fines is minimized, anddoes not significantly diminish the yield of spacer particles within thetarget particle size and having the desired particle size distribution.

The polymer particles of the present invention may be used as spacers inliquid display devices due to their narrow particle size distributionand the physical characteristics. Such liquid display devices are knownin the art and described in the literature. Typical liquid crystaldisplay arrangements are described in PCT 92/06402 and U.S. Pat. No.5,231,527. Liquid crystal display arrangements of the present inventioncomprise two sheets of substrates disposed opposite to each other; withtransparent electrodes disposed on each of said substrates andorientation films disposed over transparent electrode, the spacerparticle of the present invention and a liquid crystal layer disposedthe orientation films.

The area occupied by a spacer in a liquid crystal display does notcontain any liquid crystal, the liquid crystal layer will be displacedby the spacer particle. Accordingly, a clear spacer will scatter somelight and appear as a white area. This white area will increase thebrightness of the display in the off-state (when no light is beingtransmitted through the display) and thus reduce the contrast betweenthe on-state and the off-state. One mechanism to improve the contrast isto use a black, or other darkly colored, spacer. Thus, when theparticles of the present invention are used as spacers, it is preferredthat they are colored. In a most preferred embodiment the spacers arecolored black. Typical methods for coloring the spacer particles includestaining, pigment mixing, and the addition of dyes to monomers prior topolymerization. Other techniques known in the art include imbibingcolorants into the spacer particles or the reactive coupling of acolorant and the spacer particle. A preferred method of coloring thespacer is the reactive coupling of a colorant to a spacer particle.

In an especially preferred embodiment of the present invention theparticle is provided with adhesive properties. Polymer particles havingadhesive properties are especially useful in the field of liquid crystaldisplays. The adhesive properties aid in keeping the substrates frombecoming misaligned from one another in the manufacturing process andalso provide adhesion between the substrates after the manufacturingprocess. The adhesive properties may also reduce the movement of thespacers on the substrates and thereby reduce the potential for, or theamount of, damage to the substrates or coatings on the substrate.

There are known mechanisms for obtaining adhesion between articles, oneis through the use of reactive coupling to create bonds and another isthrough the use of thermoplastic materials known in the art. Reactivecoupling is a process of creating a chemical bond between two articlesthrough the generation of reactive functional groups. Reactivefunctional sites are amenable to chemical bond formations, including butnot limited to free radical, acidic, basic, and cationic sites. Methodsfor generating reactive functional sites can include UV radiation,thermal activation and other known processes.

A preferred embodiment of the present invention employs UV radiation togenerate free radicals. It is believed that UV-cure adhesives adhere twosurfaces through the following process: a) a spacer particle containingadhesive properties is exposed to ultraviolet radiation such thatcertain molecules within the adhesive create free radicals, and b) thefree radicals form covalent bonds with reactive groups contained withinthe coatings on the substrate (for example, the alignment layer in aliquid crystal display) but may also form covalent bonds with reactivegroups contained within the adhesive and also within the spacer particlein areas not having adhesive properties.

It is believed that thermal-cure adhesives adhere two articles through aprocess different from that of UV-cure adhesives. It is further believedthat thermal-cure adhesives adhere articles through the followingprocess: a) a spacer particle containing an adhesive layer, whereby theadhesive layer comprises a thermoplastic resin, is heated generally to atemperature above the glass transition temperature of the thermoplasticresin contained within, or substantially comprising, the adhesive layer,and b) the thermoplastic resin melts or otherwise deforms to form anattachment to the article, or coatings on the article, through amechanism believed to entail intercalation, or pore-filling, of thethermoplastic adhesive material into pores or irregularities in thesurface of the article or coatings on the article.

In an especially preferred embodiment, reactive coupling, preferably thegeneration of free radicals from UV absorption, is employed incombination with a thermoplastic adhesive. An improvement of using boththermal-cure and UV-cure adhesives is the curing rate of the adhesivecan be accelerated during the assembly of the liquid crystal display. Anadditional improvement of using both thermal-cure and UV-cure adhesivesis the added adhesive strength afforded to the system by multiple pointsof contacts between the spacer and the substrates and the multiplemechanisms for achieving said contact being both thermoplastic andreactive coupling.

Suitable materials for use as thermoplastics include poly(meth)acrylate,polyolefins, polyurethanes and the like.

Suitable materials for use in reactive coupling include aryldiazoniumsalts, diarylhalonium salts, triarylsulfonium salts, epoxides,anhydrides, carboxylic acids, hydroxy-containing compounds, amines,nitrobenzyl esters, sulfones, phosphates, n-hydroxyimide sulfonates,cobalt-amine and alkyl amine salts, O-acyloximes anddiazonaphthoquinones. A preferred embodiment is the use of reactivecoupling agents which can be incorporated into a polymer. An especiallypreferred embodiment is the use of2-hydroxy-(3-methacryloxy)-propyl-1-(2-benzoyl) benzoate, which isavailable from the Rohm and Haas Company.

The present invention, in a highly preferred embodiment, provides for amechanism to incorporate a spacer with a thin layer or coating on theouter-most surface of the spacer, also known as a vicinal layer, havingadhesive properties, containing both reactive coupling andthermoplastics, such that the vicinal layer is a part of the spacer andis distinguishable from a coating contacting the surface of the spaceras previously disclosed in the art. The vicinal layer includes from 0.1to 90 weight percent reactive coupling moieties and from 10 to 99.9weight percent thermoplastic.

In another embodiment of the present invention conductive materials areapplied to the surface of the spacer. The conductive material may be aconductive polymer, intrisinically conductive polymer, doped polymers,and metals. Suitable conductive polymers include polymers such aspolyacrylonitrile butadiene styrene, polyvinyl chlorides,polyphenylene-based alloys, or polycarbonate blended with one or moreanionic compounds to instill conductivity such as alkali salts, nonioniccompounds such as fatty acid esters and cationic compounds such asquaternary ammonium salts. Suitable intrisinically conductive polymersinclude, but are not limited to: polythiophene, polypyrrole,poly(phenylenesulfide), poly(phenylenevinylene), polyacetylene,polyaniline and polyisothianaphthene. Suitable doped polymers includesuch as polyacetylene doped with either I₃ ⁻or Na⁺; polypyrrole dopedwith BF₄ ⁻ or ClO₄ ⁻; polythiophene doped with BF₄ ⁻, ClO₄ ⁻, or FeCl₄;polyazulene doped with BF₄ ⁻ or ClO₄ ⁻; and polythienylenevinylene dopedwith AsF₅. Suitable metals include highly conductive species such as,but not limited to: copper, nickel, aluminum, gold and the like.Especially preferred is gold. Suitable methods for coating spacerparticles with conductive materials are set forth at length in WO9206402.

The particles of the present invention possess a number of improvedproperties as compared to known particles. For example, the presentparticles have enhanced mechanical properties such as improvedcompression strength, recovery factors and improved resistivity ascompared to known particles. Other improved properties includerefractive index and coefficient of thermal expansion.

Compression strength is the amount of force the particle can withstandbefore it crushes. The particles of the present invention have acompression strength of greater than 150 kilograms per square millimeter(kg/mm²). This compression strength value is sufficiently high such thatthe spacer particles do not fracture or crush during the cell-sealingprocess. In addition to high compression strength, the present particlespossess a higher initial load compression strength than known spacerparticles. Such a high initial load compression strength, also known asthe compression strength at 10% deformation of the particle, isimportant as it allows for the use of fewer particles in liquid crystaldisplays. This is very advantageous as fewer “foreign” materials will bepresent that could adversely affect the contrast between the “on” and“off” states.

The hardness (K value) of the polymer particles of the present inventionis typically greater than 600 kg/mm²; preferably greater than 625kg/mm²; more preferably greater than 650 kg/mm²; and even morepreferably greater than 700 kg/mm². It is preferred that the hardness ofthe polymer particles is in the range of 600 to 900 kg/mm²; andpreferably in the range of 625 to 875 kg/mm².

The particles of the present invention, when used as spacers, providerecovery factors of greater than 35 percent, preferably greater than 38percent and most preferably greater than 40 percent, and even morepreferably greater than 45 percent. Typically, the recovery factor is inthe range of 35 to 60 percent. Recovery factors are importantmeasurements because during cell sealing processes, typically, the twoopposing substrates are compressed and the spacers must compressslightly with pressure and re-expand upon releasing the pressure. Therecovery factor can be used to predict the cell-gap maintained after thecell-assembly process.

The resistivity of the spacers is also greatly improved by the spacersof the present invention. The spacers have resistivity of greater than4.0×10¹⁵ ohm-cm, Preferably the resistivity is greater than 5.0×10¹⁵ohm-cm. High resistivity is important in a spacer for liquid crystaldisplays. The liquid crystal molecules allow the transmission of lightthrough a display in response to an electric field. Material within theliquid-crystal layer degrading the dielectric property of the liquidcrystal layer, or alternatively increasing the conductivity of theliquid crystal layer, will adversely affect display performance.

The coefficient of thermal expansion of the spacers is also greatlyimproved by the spacers of the present invention. The spacers havecoefficients of thermal expansion greater than 100×10⁻⁶/° C. and lessthan 125×10⁻⁶/° C. Preferably the coefficient of thermal expansion isgreater than 110×10⁻⁶/° C. and less than 120×10⁻⁶/° C. The coefficientof thermal expansion of a spacer will define, in part, the spacersability to expand and contract in response to temperature. Ideally, thecoefficient of thermal expansion of a spacer will match that of theliquid crystal layer such that when the liquid crystal display isexposed to thermal cycling the expansion and contraction of the spacerparticle will match the expansion and contraction of the liquid crystallayer. Sufficient mismatch of the coefficient of thermal expansionbetween that of the spacer and that of the liquid crystal layer mayresult in the formation of voids upon thermal cycling and adverselyaffect display performance.

The index of refraction of a spacer is ideally matched to that of thesubstrate. The index of refraction for a glass substrate used in aliquid crystal display is in the range of 1.53 to 1.55. The spacers ofthe present invention have refractive indices of about 1.50.

The polymer particles of the present invention have a modulus ofelasticity in compression of greater than 500 kg/mm². The modulus ofelasticity is preferably greater than 520 kg/mm²; more preferablygreater than 550 kg/mm²; and even more preferably greater than 600kg/mm². Particularly useful ranges of the modulus of elasticity are 520to 800 kg/mm²; preferably 550 to 750 kg/mm²; and more preferably 600 to750 kg/mm².

The following examples are intended to illustrate the process by whichthe compositions of this invention are made, the compositions of thisinvention, and the unexpected beneficial properties of the compositionsof this invention when applied as spacers in liquid crystal displays.

EXAMPLE 1: COMPARATIVE

In this example the 0.69-micron seed particles prepared according toExample 2 of U.S. Pat. No. 5,846,651 (Wu) were grown to 5.00 microndiameter using an emulsion of 1,6-hexanediol diacrylate. The followingmixtures were prepared:

Parts by Mixture Component Weight A water 160 3% aqueous Solusol ®(available from American 1.52 Cyanamid Fine Chemical Div.) B Seedemulsion (0.69 μm) at 6.73% solids 3.86 water 12.5 C 1,4-hexanedioldiacrylate (“HDDA”) 100 50.8% aqueous methyl beta-cyclodextran 1.56 75%aqueous Solusol ® 0.81 water 89.0 D tert-Butyl peroctoate 0.50 3%aqueous Solusol ® 3.33 0.11% aqueous sodium p-nitrosophenolate 1.48water 10.0 E 30% aqueous poly(n-vinylpyrrolidone) 16.7 water 6.25

Mixture A was added into a reactor and heated to 65° C. with stirring.Mixture B was then added into the reactor. Mixture C was blended by anOMNI homogenizer for 5 minutes to form an emulsion and then added intothe reactor. The reactor was stirred at 60° C. for 2 hours and thencooled to 25° C. The stirring was continued overnight. Mixture D wasblended by an OMNI homogenizer for 3 minutes to form an emulsion. Thisemulsion was added to the reactor and followed by the addition ofMixture E. After 1 hour stirring at 25° C., the reactor was heated to60° C. and held for 1 hour at 60° C. before heating to 90° C. Stirringwas continued at 90° C. for 1 hours, after which the reactor contentswere cooled to room temperature for filtration through a Nylon clothhaving 125-μm openings.

The filtered mixture was transferred into a pressure reactor. Withstirring turned on, the reactor was heated to 100° C. After heating at100° C. for 1 hour, the reactor was heated to 180° C. in 3 hours. Afterheating at 180° C. for 1 hour, the reactor was cooled to roomtemperature and filtered through a Nylon cloth having 125-μm openings.

The polymer particles, pHDDA, from the reaction mixture, when examinedby an optical microscope, were uniformly sized and were 5.00 microns.

EXAMPLE 2

Polymer particles were prepared according to Example 1 except that theHDDA was replaced with a mixture of 50 parts of divinylbenzene (“DVB”)and 50 parts of HDDA. The resulting polymer particles, p(DVB 50/HDDA50), were uniformly sized and had a particle size of 5.00 microns.

EXAMPLE 3

Polymer particles were prepared according to Example 1 except that theHDDA was replaced with a mixture of 75 parts of DVB and 25 parts ofHDDA. The resulting polymer particles, p(DVB 75/HDDA 25), were uniformlysized and had a particle size of 5.00 microns.

EXAMPLE 4

Polymer particles were prepared according to Example 1 except that theHDDA was replaced with a mixture of 88 parts of DVB and 12 parts ofHDDA. The resulting polymer particles, p(DVB 88/HDDA 12), were uniformlysized and had a particle size of 5.00 microns.

EXAMPLE 5

The polymer particles prepared according to Examples 1-4 were tested forinitial compression strength at 25° C. The load at 10% deformation ofindividual spacers was determined on a micro-compression testinginstrument from Shimadzu Scientific Instruments Inc., model number isMCTM-500. The results of the tests are reported in Table 1.

TABLE 1 Load at Polymer Particles Composition, Wt % 10% DeformationIdentification Size, μm HDDA DVB gram force Example 1 5.00 100 0 0.123(comparative) Example 2 5.00 50 50 0.147 Example 3 5.00 75 25 0.163Example 4 5.00 88 12 0.172

The above results demonstrate the compositions of this invention haveimproved compression strength at initial deformation over known polymerparticles.

EXAMPLE 6

Polymer particles were prepared according to Example 1 except that theHDDA was replaced with a mixture of 25 parts of DVB and 75 parts ofHDDA. The resulting polymer particles, p(DVB 25/HDDA 75), were uniformlysized and had a particle size of 4.00 microns.

EXAMPLES 7-8

Polymer particles were prepared according to Example 1 except that theHDDA was replaced with a mixture of DVB and 1,4-butanediol diacrylate(“BDDA”). The amounts of DVB and BDDA used and the particle sizes of theresulting polymer particles are reported in Table 2.

TABLE 2 Example DVB, wt % BDDA, wt % Particle Size (μm) 7 88 12 4.5 8 7525 4.5

EXAMPLE 9

This example shows the formation of adhesives onto the polymer particlesof in the emulsion of Example 6. The following mixtures were prepared:

Mixture Component Parts by Weight F Emulsion from Example 5 at 24.97%solids 1732 water 374 G Sodium formaldehyde sulfoxylate 1.62 water 251 HMethylolacrylamide and acrylamide (45% 18.0 aqueous solution from Rohmand Haas Company) water 108 I 1,6-Hexanediol diacrylate 0.22 n-Butylmethacrylate 10.8 Styrene 89.0 water 74.8 J tert-Butyl hydroperoxide70X ® (from 2.43 Lucidol Division of Pennwalt Corp.) 3% aqueousSolusol ® 3.60 water 195

Mixture F was added into a reactor and heated to 70° C. with stirring.One half of Mixture G was then charged into the reactor. The second halfof Mixture G, and Mixtures H, I, and J were evenly added into thereactor over 5 hours. Stirring was continued at 70° C. for 1 hour, afterwhich the reactor contents were cooled to room temperature and filteredthrough a Nylon cloth having 125-μm openings. The polymer particles fromthe reaction mixture, when examined by an optical microscope, were foundto be uniformly sized.

EXAMPLE 10

This example demonstrates the formation of a conductive coating on 5.00micron particles of p(DVB 88/HDDA 12).

A 50 ml beaker was charged 1.00 gram of cleaned 5.00-micron particles ofp(DVB 88/HDDA 12). Conditioner PM-922 (Shipley Company) of 30 ml heatedto 49° C. was charged into the beaker. The suspension was stirredintermittently with a glass stir rod and the beaker was placed on a hotplate to maintain the temperature. After 5 minutes the polymer particleswere isolated by filtration from the solution using a.0.45 micron filterdisk (Micron Separation Inc.). They were rinsed 3 times with 20 mlportions of deionized water. The particles were then charged into a 50ml beaker along with 30 ml of Neutralizer PM-954 (Shipley Company) froma heated reservoir maintained at 32° C. The suspension was placed on ahot plate to maintain the temperature and stirred intermittently for 5minutes. The particles were then collected and washed 3 times with 20 mlportions of deionized water. The particles were charged into a 50 mlbeaker along with 30 ml of Cataposit 44® (Shipley Company) and heated to32° C. The suspension was placed on a hot plate to maintain thetemperature and stirred intermittently for 4 minutes. The particles werecollected and washed 3 times with 20 ml portions of deionized water. Thepolymer particles were charged into a 50 ml beaker again and then 30 mlof Accelerator 19 (Shipley Company) heated to 32° C. was added. Thesuspension was placed on a hot plate to maintain the temperature andstirred intermittently for 3 minutes. Then the sample was collected byfiltration and washed three times with 20 ml aliquots of deionizedwater. The sample was again charged into a 50 ml beaker and then 30 mlof Niposit® Electroless Nickel PM-980 (Shipley Company) heated to 27° C.was added. The suspension was stirred for 3 minutes and the beaker wasplaced on a hot plate to maintain the temperature. Upon addition of theElectroless Nickel solution a reaction occurred and the polymerparticles turned from white to gray. The polymer particles were isolatedand washed an additional three times with deionized water to completelyremove any unreacted nickel salts or reducing agent. The samples werethen dried in an oven at 40° C. to yield 0.92 g of a gray powder ofcoated polymer particles.

Under an optical microscope a metallic, a mirror-like coating on theparticles could be observed. The samples was analyzed by energy dispersex-rays using a PGT analyzer on an Electroscan environmental scanningelectron microscope. Nickel was detected on the coated particles.

EXAMPLE 11

The polymers of Examples 4 and 7 were tested for physical properties.The results are listed in Table 3.

TABLE 3 Property Example 4 Example 7 Form Remarks Compressive Strength,10 9.5 block ASTM D695 kg/mm² 310 320 Compression Elastic Modulus,kg/mm² Specific Gravity 1.08 1.08 sheet ASTM D792 Thermal Expansion 5.45.6 sheet ASTM D696, Coefficient, 10⁻⁵/° C. modified for average 20˜80°C. Volume Resistivity, 1.0 1.0 sheet ASTM D257 10¹⁷ Ohm cm DielectricConstant, 2.7 2.7 sheet ASTM D150 1 kHz Dielectric Dissipation 0.00800.0073 Transmittance 91% 90% sheet ASTM Haze 1.0% 0.8% D1003 RefractiveIndex 1.59 1.59 sheet

EXAMPLE 12

The polymer particles of the present invention were evaluated todetermine their elastic modulus, harness, and recovery factor. Theelastic modulus and hardness were calculated using the formulaedisclosed in U.S. Pat. No. 5,486,941 (Saiuchi et al.) and U.S. Pat. No.5,231,527 (Takanashi et al.). These data are reported in Table 4.

TABLE 4 Particle Size Recovery Example (μm) Elastic Modulus HardnessFactor (%) 3 5.0 529 619 44 3 4.5 574 671 41 4 4.1 588 687 40 4 4.5 600701 37 4 6.0 521 609 52 8 4.5 640 748 44 9 3.4 732 856 39

What is claimed is:
 1. A liquid crystal display containing a spacerparticle formed from a copolymer of 1 to 30% wt of a multifunctional(meth)acrylate monomer and 70 to 99% wt of a multifunctional aromaticmonomer, wherein the multifunctional (meth)acrylate monomer is a(C₂-C₁₈)alkanediol di(meth)acrylate.